1. Field of the Invention
The present invention relates to an improved ink jet recording method applicable, for example, to printers using ink jet methods, high-speed business printers, apparatuses for printing on plastic films, and label printing apparatuses, an ink jet recording apparatus, and an ink jet recorded matter.
2. Description of the Related Art
Ink jet recording technology is a technique that brings ink to liquid droplets through micronozzles using a pressure on-demand method, a charge control method and the like and deposits the liquid droplets on a recording medium such as paper according to image information. The ink jet recording technology is suitable for use in image forming apparatuses such as printers, facsimile machines, and copying apparatuses. According to the ink jet recording technology, ink is deposited directly on a recording medium to form an image, and, thus, recording can be performed in a simpler apparatus construction than in indirect recording using photoreceptors such as electrophotographic recording. This would lead to further development of the ink jet technology as a method for recording image on recording media in the future.
The ink jet recording method is a low-noise printing method, and a method (a direct ejection method) is mainly used that directly ejects ink on recording media such as papers, cloths, and plastic sheets according to image signals to print characters, images and the like. Further, in the ink jet recording method, any plate is not necessary in printing. Accordingly, printed matters can be efficiently prepared even when the number of printed matters is small. Thus, the ink jet recording method is also expected in industrial applications. When the ink jet recording method is used in industrial applications, images should be formed on various recording media. The direct ejection method that is mainly used cannot satisfy this point.
Specifically, in the ink jet recording method by the direct ejection method, there is a limitation that the method is likely to be influenced by recording media.
More specifically, due to a difference in ink absorption and in wettability by ink between recording media, way of spreading, way of feathering or bleeding, and way of connection to adjacent dots vary. Accordingly, the image quality is likely to be influenced by recording media, and, thus, it is difficult to form stable images on various recording media. For example, for ink-absorptive recording media such as papers, ink droplets are deposited on an ink-absorptive recording medium such as paper and are permeated into the recording medium within several milliseconds. In this case, the permeation proceeds along paper fibers and the like. Thus, feathering of the ink or bleeding between different color inks occurs, and the formation of high-quality images is sometimes inhibited.
Accordingly, various measures have hitherto been proposed. However, it is still difficult to say that they are satisfactory. For example, techniques related to an ink jet recording method and an ink jet recording apparatus in which, after semi-curing of a photocurable pretreating agent on a recording medium, a photocurable ink is ejected by an ink jet method to form an image have been proposed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2008-105382). According to this proposal, an undercoating layer is semi-cured before the ejection of the ink, and excessive spreading of ink droplets is prevented by the semi-curing. However, conditions for the preparation of the semi-cured state are difficult, and, for example, uneven curing of complete curing in one portion and little or no curing in another portion occurs. The uneven curing poses a difference in spreading of ink droplets.
Japanese Patent Application Laid-Open (JP-A) No. 2004-42548 proposes an ink jet recording method that includes providing an energy beam curable color ink as ink, ejecting the energy beam curable color ink on a recording medium to form ink dots, irradiating the ink dots with energy beams according to ejection timing to thicken and precure the dots to such an extent that adjacent dots are not mixed together, then further irradiating the precured dots with energy beams to fully cure the dots. This proposed method can suppress feathering or bleeding but poses a problem that images are different among various recording media.
Japanese Patent Application Laid-Open (JP-A) No. 2004-244624 proposes an ink jet recording method that includes ejecting ink containing a cationically polymerizable ingredient curable with an actinic radiation on a recording medium through an ink jet recording head to deposit dots on the recording medium, and then irradiating the dots with an actinic radiation to cure the dots and thus to form an image, wherein a requirement of A≦B is satisfied wherein A represents a value of surface tension 1 of the ink, mN/m; and B represents surface tension 2 of the ink, mN/m. According to this proposal, high-definition images possessing anti-feathering, even density, and excellent smoothness of the formed images are obtained. However, it should be noted that, in this proposal, a relative surface tension difference between one pretreating liquid and color ink is merely compared and it is difficult to simultaneously meet various attributes of a wide variety of images.
On the other hand, when recording media such as films that do not absorb ink are used, drying by permeation is impossible and, thus, for example, ink that dries through vaporization of a solvent used, ink that is solidified by a phase change, and photopolymerizably curable ink are used. The fact that the shape and area of formed image dots vary depending upon the wettability of the recording medium by the ink poses a problem of stable formation of high-quality images. For example, a (beading) phenomenon that, in printing (solid image) on films having a surface that is less wettable by ink, ink droplets that have been previously deposited are attracted by ink droplets that have been deposited later are likely to occur, making it difficult to obtain even images when ink dots such as solid images are densely formed.
The surface treatment of the recording media can allow the recording media to be wetted by ink. On the other hand, when the recording media are likely to be wetted, dot feathering is likely to occur and pixels are spread. Accordingly, this technique is suitable for solid image formation but suffers from a problem that fine and high-definition expression is impossible.
Japanese Patent Application Laid-Open (JP-A) No. 2008-246837 proposes an ink jet recording method that includes an undercoating liquid application step of applying an undercoating liquid on a recording medium; a white ink application step of applying a white ink containing a white pigment; a curing step of semi-curing the applied undercoating liquid and white ink; and a recording step of ejecting an ink curable by actinic radiation irradiation on the semi-cured undercoating liquid and white ink to record an image.
Japanese Patent Application Laid-Open (JP-A) No. 2004-42525 proposes a method that includes evenly coating a radiation curable white ink as an undercoating layer on a transparent or semi-transparent recording medium, solidifying or thickening the coating by radiation irradiation, and then performing ink jet recording with a radiation curable color ink set. This proposal can reduce the problems of visibility of color inks, feathering or bleeding, and a difference in images among various recording media, but on the other hand, is unsatisfactory for eliminating uneven line widths, uneven colors or other problems attributable to mixing among liquid droplets.
When inks are overprinted, at a glance it seems that dense solid images can be formed. In fact, however, the thickness of the ink is increased, and surface concaves and convexes are increased in printing of general reactive inks, posing a problem that the optical density is disadvantageously lowered by irregular reflection.
There is a method that solid image expression and high-definition image expression are simultaneously realized by increasing the number of dots using small ink droplets. When high-speed printing is performed, small ink droplets ejected through nozzles are likely to be susceptible to an influence of wind produced in paper conveying or the like and ink deposition positions are unstable, making it difficult to form high-definition images.
Thus, in image recording on various recording media, simultaneous realization of high-density solid images and fine and high-definition image expression are difficult.
Accordingly, the provision of an ink jet recording method and an ink jet recording apparatus that can realize the formation of images having a high quality, that is, that, even when various recording media different from each other in ink absorption and wettability by ink are used, can realize high image evenness among various recording media, can effectively suppress ink feathering, can suppress the occurrence of uneven line widths and uneven colors attributable to mixing among liquid droplets, can realize high optical density expression that has little or no surface concaves and convexes and surface scattering even in high-density expression (solid image) portions having a high ink pixel density and, at the same time, can realize fine characters and expression of high-resolution and high-definition portions have been desired.